Does someone have to show their cards at the end of a hand? For example I bet the the turn or river in a small stakes tourney and he called and at the end he showed his cards and I mucked because I lost, but he demanded to see my cards can the dealer unmuck the cards and show him? This was at a small stakes undergound poker room during a tourney and the rules might not be exact.

in a tournament he can ask to see your hand. you should then ask why he thinks you're colluding

It is generally considered poor form to ask to see the hand of a player who is mucking after being called. It is allowed (the rule is usually abbreviate IWTSTH or 'I want to see that hand'). In typical application, any player who has a live hand at showdown can ask to see other players hands that were live at showdown. Some rooms allow any player who was involved in the hand to ask.

Typically the bad blood you generate from this request is not worth the very marginal amounts of information you can glean from seeing their mucked hand

If you really want to see the other player's cards, and if the other player is obligated to show first, just wait for the other guy to show first. If he is reluctant, you can say "show or muck" and if he mucks his cards, then you win regardless of what you have. In some rooms, you can rake in the pot without showing your own cards (if you care not to).

If he called you, and then he showed his cards without forcing you to show first and you mucked, he can ask the dealer to fish the mucked cards out if they are still identifiable and show him - it's out of your hands.

I call this the "Once a month rule" since it's really not a good thing to do ... and a Floor could take the option away from you if you do it 'too often'.

Typically a player is just curious to see how you play. If you are first to show, just show your cards and move on. Certainly it can be a bit 'embarrassing' that you got caught bluffing but that's part of the game.

The 'collusion' tag usually comes from someone not involved in the showdown who might think you are chip dumping when you muck. The other thing to consider is that typically if an opponent who is in the showdown asks to see your hand it will still be a live hand, thus if you misread your hand and it shows to be a winner then you will take the pot away from them ... possibly with strange looks from the table.

There is a thread here somewhere where 2 guys were over using this option and a player set them up by trying to muck knowing that they would insist on seeing his cards. The Dealer turned over a winning full house ... Neither player requested to see cards the rest of the night!! GL